[Virtio-fs] [PATCH 4/4] virtiofsd: use fallocate(2) instead posix_fallocate(3)

[Miklos Szeredi]

On Wed, Apr 17, 2019 at 3:18 PM Dr. David Alan Gilbert
<dgilbert at redhat.com> wrote:
>
> * Liu Bo (bo.liu at linux.alibaba.com) wrote:
> > From: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
> >
> > This is because posix_fallocate(3) does not support FALLOC_FL_KEEP_SIZE
> > and FALLOC_FL_PUNCH_HOLE. Our underlying host filesystem is ext4 and
> > ext4 supports FALLOC_FL_KEEP_SIZE and FALLOC_FL_PUNCH_HOLE well, so
> > this change will be ok.
> >
> > Signed-off-by: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
>
>   We need to check what 'fuse' expects - is it defined what
> fallocate features it has, and what the semantics are?

The patch looks good to me.

Fuse (the kernel part) supports FALLOC_FL_KEEP_SIZE and
FALLOC_FL_PUNCH_HOLE, but returns EOPNOTSUPP for any other flag.

Even if, at a later time, fuse starts supporting additional fallocate
flags, then the passthrough implementation calling fallocate(2) should
be fine.

Thanks,
Miklos